1. Technical Field
The present invention is related to a capacitive touch panel, more particularity, to a control circuit and control method for a capacitive touch panel.
2. Description of Related Art
Capacitive touch panels are lightweight, compact, power saving, and durable so as to be widely used as panels of notebook computers, cell phones, personal digital assistants, and multimedia players. Typically, a capacitive touch panel comprises a printed circuit board, a piece of glass, or a plastic film as a substrate. A conductive film of metal or indium tin oxide or a pattern made of other materials is printed on the substrate as sensors, whose shapes and sizes vary with intended applications. When the touch panel is touched by a stylus or a user's finger, change in capacitance takes place at the sensors. A control circuit detects the changes of capacitance at the sensors to obtain information input by the user and thus enable touch control. Therefore, a conventional technique for enhancing performance of a touch panel is to increase the change of capacitance (ΔC) resulting from contact by a conductor. For instance, U.S. Pat. No. 5,920,309 proposes a control method for a capacitive touch panel wherein antiphase current signals are used to charge and discharge adjacent sensors so that change of capacitance is augmented differentially, thereby improving performance of the touch panel.
However, in addition to the change of capacitance (ΔC), the performance of a capacitive touch panel is related to its base capacitance (CBASE). When the base capacitance is high, the change of capacitance is less apparent and therefore difficult to detect, which leads to low performance. In other words, the performance of a capacitive touch panel is in direct proportion to ΔC/CBASE. The conventional differential detection method, though capable of increasing change of capacitance, also increases parasitic capacitances between adjacent sensors. As a result, the capacitive touch panel has a high base capacitance, and there is limited room for improvement of performance.